The invention relates to a process for the desulphurization of a pig iron melt which is to be further processed into steel in an oxygen top blowing converter wherein the melt is poured into a ladle and brought into contact with a solid slag that contains calcium oxide which accumulates in the steel manufacturing process as well as other desulphurization agents.
A general process for the desulphurization of pig iron is known from DE 38 36 549 C1. In this process, the converter slag that accumulates during the oxygen top blowing process is used as the desulphurization slag. The converter slag in molten form is optionally poured directly from the converter into the treatment ladle intended to accommodate the pig iron, and then the pig iron is poured onto the slag. Alternatively, it is proposed that converter slag, after having been poured from the converter, is cooled and processed into small pieces with a maximum piece size of 50 mm, and is then added to the pig iron in this form. A disadvantage of this known process is that the converter slag has a low sulfide capacity, so that the amount of additional expensive desulphurization reagents required is still very high.
DE 88 16 829.8 U1 discloses a mixture of calcium carbide and magnesium as an agent for the desulphurization of pig iron melts. To ensure good dosability during injection, and to prevent separation even during long periods of standing or during transport, it is proposed that the bulk weight and grain size of the two components be in the same range. In a preferred embodiment, the two components are coated with an oily liquid. This reduces the possibility of separation and permits even more precise dosing.
The object of the present invention is to provide a process for the desulphurization of pig iron, in which the relative amount of the usual expensive desulphurization reagents, such as calcium carbide and magnesium, is significantly reduced and the amount of slag to be deposited and disposed of is decreased.